In connecting sewer pipe to manholes, various techniques are employed. Some of these are discussed in my above-mentioned U.S. patent.
In many of the prior art devices available, a clamping ring, generally of metal construction (similar to a radiator clamp) is used to clamp a part of the gasket to the pipe, in order to prevent passage of water through the manhole wall, at that point in the wall in which a pipe communicates with the interior of the manhole.
In the invention of my above-identified patent, I eliminated the separate clamp as such, and utilized a pair of rings for effecting a good sealing condition between the pipe and the wall of the manhole.
In the more-recent invention of my above-mentioned patent application, I disclosed a gasket which was an improvement in terms of labor saving, as well as in terms of simplicity and ease of construction, and which especially is an easy device to assemble, in that it minimized the number of parts, requiring only a gasket.
However, in some instances, the joint between the pipe and the manhole is subjected to significant pressures, which instances are prone to cause leakage around the pipe, through the manhole wall. Such instances can include situations in which high ground water, or an increased water table causes a pressure head outside the manhole, keeping a high and constant pressure on the joint. In many such situations, it is undesirable to have ground water leaking into the manhole, so as to inhibit the ability of the manhole to carry away water that it is intended to receive via pipes.
Accordingly, the present invention is directed toward providing the ability of the gasket assembly to withstand high water pressures, and to permit a highly-effective water-tight seal under conditions in which the seal is subjected to high exterior pressures that may otherwise tend to promote leakage.